1. Field of the Invention
The present invention relates to a wire bonding apparatus.
2. Prior Art
A conventional wire bonding apparatus is shown in FIG. 3.
A spool 2 with a bonding wire 1 wound around it is attached to a spool holder 3, and this spool holder 3 is rotated by a spool-rotating motor 4. One end of the bonding wire 1 is passed through a wire-cutting clamper 5 and then a capillary 6, while the other end of the bonding wire 1 is connected to the ground terminal 7 of the spool holder 3. A wire slack forming means 8 which includes a nozzle for blowing air against the bonding wire 1 is installed above the wire-cutting clamper 5. The wire slack forming means 8 creates slack in the bonding wire 1 and causes the ball 1a formed at the tip of the bonding wire 1 to come in contact with the capillary 6. The wire slack forming means 8 can suck the air instead of blowing the air to the bonding wire 1.
An electric torch power supply 10 for forming the ball 1a on the bonding wire 1 by applying a high voltage to the bonding wire is connected to the wire-cutting clamper 5 via an electric torch 11 and a switch 12. In order to detect faulty wire connections, a slip ring 14 is mounted on the spool shaft 13 of the spool holder 3, and a power supply 15 used for the detection of faulty wire connections is connected to the slip ring 14 via the switch 12. Faulty wire connections are detected by a faulty wire connection detector 16. Thus, the switch 12 is connected to the electric torch power supply 10 only during the formation of the ball 1a.
Japanese Patent Application Laid-Open (Kokai) No. 2-298874 discloses an example of the faulty wire connection detecting means.
The above described bonding apparatus operates in accordance with the time chart shown in FIG. 4.
FIG. 4a shows the timing of the raising and lowering of the capillary 6, FIG. 4b shows the timing of the opening and closing of the wire-cutting clamper 5, FIG. 4c shows the timing of the wire feeding, i.e., the operation of the spool-rotating motor 4, FIG. 4d shows the timing of the formation of the ball 1a, and FIG. 4e shows the timing of the detection of faulty wire connections.
First, the switch 12 is operated so as to be connected to the electric torch power supply 10. A high voltage is applied from the electric torch power supply 10 to the electric torch 11 and also to the bonding wire 1 that passes through the wire-cutting clamper 5. Thus, the ball 1a is formed at the tip of the bonding wire 1 by the discharge of the electric torch 11. After the ball 1a has thus been formed, the switch 12 is connected to the power supply 15 used for the detection of faulty wire connections.
The capillary 6 is next lowered, and the ball 1a is bonded to the first bonding point (called "first bond"). Afterward, the capillary is raised and moved to a position above the second bonding point and then again lowered.
During this period, a voltage is applied to the bonding wire 1 by the power supply 15 used for the detection of faulty wire connections via the slip ring 14, spool shaft 13, spool holder 3 and ground terminal 7. Thus, the bonding condition at the first bonding point is detected. If the wire connection is normal, the lowering of the capillary 6 is continued, and the bonding wire 1 is bonded to the second bonding point (called "second bond").
Afterward, the wire-cutting clamper 5 is closed, and the capillary 6 is raised. When the capillary 6 has been raised to a predetermined height, the wire-cutting clamper 5 is raised, and the bonding wire 1 is cut at a bonded point base of the second bonding point. During the period between the completion of the second bond and the cutting of the bonding wire, a voltage is applied to the bonding wire 1 by the power supply 15 used for the detection of faulty wire connections, and the bonding at the second bonding point is detected.
As seen from the above, the bonding wire 1 must be electrically connected to the electric torch power supply 10 when the ball 1a is formed. In addition, the bonding wire 1 must be electrically connected to the power supply 15 used for the detection of faulty wire connections when faulty wire connections are detected.
In these cases, the electrical connection of the electric torch power supply 10 to the bonding wire 1 for the purpose of forming the ball 1a is accomplished via the wire-cutting clamper 5. However, the main purpose of this wire-cutting clamper 5 is to securely clamp and cut the bonding wire 1. If the wire-cutting clamper 5 is thus used for such an electrical connection for forming the ball 1a too, the wire-cutting clamper 5 may be damaged by electrical discharge phenomena that occurs between the bonding wire 1 and the wire-cutting clamper 5. This results a drop in the clamping capacity of the wire-cutting clamper 5.
Furthermore, in the prior art as described above, the electrical connection of the power supply 15 to the bonding wire 1 for detecting faulty wire connections is accomplished via the slip ring 14, spool shaft 13, spool holder 3 and ground terminal 7. Accordingly, whenever the spool 2 is changed, the bonding wire 1 must be reconnected to the ground terminal 7. Furthermore, the electrical connection to the bonding wire 1 is accomplished by the fixed slip ring 14 via the rotating spool holder 3 and spool shaft 13. Thus, the structure tends to be complex. In addition, since slipping members (slip ring, spool shaft, etc.) are used, debris tends to generate.